Solar cell and method of manufacturing the same

ABSTRACT

Discussed is a solar cell including a single crystalline semiconductor substrate having a first transparent conductive oxide layer positioned on a non-single crystalline emitter layer; a second transparent conductive oxide layer positioned over a rear surface of the single crystalline semiconductor substrate; a first electrode part including a first seed layer directly positioned on the first transparent conductive oxide layer; and a second electrode part including a second seed layer directly positioned on the second transparent conductive oxide layer, wherein the first transparent conductive oxide layer and the first seed layer have different conductivities, and wherein the second transparent conductive oxide layer and the second seed layer have different conductivities.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of U.S. patent application Ser. No.12/622,185 filed on Nov. 19, 2009, which claims the benefit under 35U.S.C. §119(a) to Korean Patent Application No. 10-2008-0115121 filed onNov. 19, 2008, all of which are hereby expressly incorporated byreference into the present application.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the invention relate to a solar cell and a method ofmanufacturing the same.

Description of the Related Art

Recently, as existing energy sources such as petroleum and coal areexpected to be depleted, interests in alternative energy sources forreplacing the existing energy sources are increasing. Among thealternative energy sources, solar cells have been particularlyspotlighted because, as cells for generating electric energy from solarenergy, the solar cells are able to draw energy from an abundant sourceand do not cause environmental pollution.

A solar cell generally includes a substrate and an emitter layer, eachof which is formed of a semiconductor, and electrodes respectivelyformed on the substrate and the emitter layer. The semiconductorsforming the substrate and the emitter layer have different conductivetypes, such as a p-type and an n-type. A p-n junction is formed at aninterface between the substrate and the emitter layer.

When light is incident on the solar cell, a plurality of electron-holepairs are generated in the semiconductors. The electron-hole pairs areseparated into electrons and holes by the photovoltaic effect. Thus, theseparated electrons move to the n-type semiconductor (e.g., the emitterlayer) and the separated holes move to the p-type semiconductor (e.g.,the substrate), and then the electrons and holes are collected by theelectrodes electrically connected to the emitter layer and thesubstrate, respectively. The electrodes are connected to each otherusing electric wires to thereby obtain electric power.

Because the electrodes respectively connected to the substrate and theemitter layer are respectively positioned on the substrate and theemitter layer, the electrodes collect the holes and the electronsrespectively moving to the substrate and the emitter layer and allow theholes and the electrons to move to a load connected to the outside.

However, in this case, because the electrodes are formed on the emitterlayer on an incident surface of the substrate, on which light isincident, as well as a non-incident surface of the substrate, on whichlight is not incident, an incident area of light decreases. Hence,efficiency of the solar cell is reduced.

Accordingly, a back contact solar cell was developed so as to increasethe incident area of light. In the back contact solar cell, all ofelectrodes collecting electrons and holes are formed on a rear surfaceof a substrate.

SUMMARY OF THE INVENTION

In one aspect, there is a solar cell including a substrate, at least oneemitter layer on the substrate, at least one first electrodeelectrically connected to the at least one emitter layer, and at leastone second electrode electrically connected to the substrate, wherein atleast one of the first electrode and the second electrode is formedusing a plating method.

At least one of the first electrode and the second electrode may includea first conductive layer and a second conductive layer on the firstconductive layer.

A density of the first conductive layer may be different from a densityof the second conductive layer. The density of the second conductivelayer may be greater than the density of the first conductive layer.

The first conductive layer may be formed of a conductive metal materialor a transparent conductive material. The second conductive layer may beformed of a conductive metal material.

At least one of the first electrode and the second electrode may havespecific resistance of about 3.3×10⁻⁶ Ωcm. At least one of the firstelectrode and the second electrode may have a width of about 10 μm to100 μm. At least one of the first electrode and the second electrode mayhave a height of about 10 μm to 20 μm.

The substrate and the at least one emitter layer may be formed ofdifferent forms of silicon.

The substrate may be formed of crystalline silicon, and the at least oneemitter layer may be formed of amorphous silicon.

The solar cell may further include a transparent conductive oxide layeron the at least one emitter layer. The at least one first electrode maybe electrically connected to the at least one emitter layer through thetransparent conductive oxide layer.

The at least one first electrode and the at least one second electrodemay be positioned on opposite surfaces of the substrate.

The solar cell may further include a first transparent conductive oxidelayer on the at least one emitter layer and a second transparentconductive oxide layer on the substrate. The at least one firstelectrode may be electrically connected to the at least one emitterlayer through the first transparent conductive oxide layer, and the atleast one second electrode may be electrically connected to thesubstrate through the second transparent conductive oxide layer.

The at least one first electrode and the at least one second electrodemay be positioned on opposite surfaces of the substrate.

The solar cell may further include at least one back surface field layeron the substrate. The at least one second electrode may be electricallyconnected to the substrate through the at least one back surface fieldlayer.

The at least one emitter layer and the at least one back surface fieldlayer may be positioned on the same surface of the substrate.

In another aspect, there is a solar cell including a substrate formed ofa first semiconductor, a plurality of emitter layers on the substrate,the plurality of emitter layers being formed of a second semiconductordifferent from the first semiconductor, a plurality of first electrodeselectrically connected to the plurality of emitter layers, and aplurality of second electrodes electrically connected to the substrate,wherein at least one of the first electrode and the second electrode isformed using a plating method.

At least one of the first electrode and the second electrode may includea first conductive layer, and a second conductive layer on the firstconductive layer.

A density of the second conductive layer may be greater than a densityof the first conductive layer.

The plurality of emitter layers and the plurality of first electrodesmay be positioned on the same surface of the substrate as the pluralityof second electrodes.

In another aspect, there is a method of manufacturing a solar cellincluding forming an emitter layer of a second conductive type oppositea first conductive type on a substrate of the first conductive type, andforming a first electrode electrically connected to the emitter layerand a second electrode electrically connected to the substrate, whereinthe forming of the first and second electrodes includes plating aconductive material to form at least one of the first and secondelectrodes, and the substrate and the emitter layer are formed ofdifferent semiconductors.

The forming of the first and second electrodes may include forming atransparent conductive oxide layer on at least one of the substrate andthe emitter layer, forming a first conductive layer on a portion of thetransparent conductive oxide layer using a direct printing method, andplating the conductive material on the first conductive layer using thefirst conductive layer as a seed layer to form a second conductive layeron the first conductive layer and thereby forming at least one of thefirst and second electrodes.

The forming of the first and second electrodes may include forming atransparent conductive oxide layer on at least one of the substrate andthe emitter layer, forming a plating resist layer on a portion of thetransparent conductive oxide layer to expose another portion of thetransparent conductive oxide layer, plating the conductive material onthe exposed portion of the transparent conductive oxide layer using theexposed portion of the transparent conductive oxide layer as a seedlayer to form at least one of the first and second electrodes, andremoving the plating resist layer.

The forming of the first and second electrodes may include forming afirst conductive layer on a portion of at least one of the substrate andthe emitter layer using a direct printing method, and plating theconductive material on the first conductive layer using the firstconductive layer as a seed layer to form a second conductive layer onthe first conductive layer and thereby forming at least one of the firstand second electrodes.

The first electrode and the second electrode may be positioned on thesame surface of the substrate.

The forming of the first and second electrodes may include forming aconductive layer on at least one of the substrate and the emitter layer,forming a plating resist layer on a portion of the conductive layer toexpose a portion of the conductive layer, plating the conductivematerial on the exposed portion of the conductive layer using theexposed portion of the conductive layer as a seed layer to form at leastone of the first and second electrodes, forming an etch stop layer on atleast one of the first and second electrodes to expose the platingresist layer, and removing the exposed plating resist layer and theconductive layer underlying the exposed plating resist layer andremoving the etch stop layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a partial perspective view of a solar cell according to anembodiment of the invention;

FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1;

FIG. 3 illustrates an example of a width and a thickness of a frontelectrode;

FIGS. 4A to 4D are cross-sectional views sequentially illustrating eachof stages in a method of manufacturing a solar cell according to anembodiment of the invention;

FIG. 5 is a partial cross-sectional view of a solar cell according toanother embodiment of the invention;

FIGS. 6A to 6E are cross-sectional views sequentially illustrating eachof stages in a method of manufacturing a solar cell according to anotherembodiment of the invention;

FIG. 7 is a partial cross-sectional view of a solar cell according toanother embodiment of the invention;

FIG. 8 is a partial perspective view of a solar cell according toanother embodiment of the invention;

FIG. 9 is a cross-sectional view taken along the line IX-IX of FIG. 8;

FIGS. 10A to 10E are cross-sectional views sequentially illustratingeach of stages in a method of manufacturing a solar cell according toanother embodiment of the invention;

FIG. 11 is a partial perspective view of a solar cell according toanother embodiment of the invention;

FIG. 12 is a cross-sectional view taken along the line XII-XII of FIG.11; and

FIGS. 13A to 13E are cross-sectional views sequentially illustratingeach of stages in a method of manufacturing a solar cell according toanother embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention will be described more fully hereinafter with reference tothe accompanying drawings, in which example embodiments of theinventions are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

A solar cell according to an embodiment of the invention is describedbelow in detail with reference to FIGS. 1 to 3.

FIG. 1 is a partial perspective view of a solar cell according to anembodiment of the invention. FIG. 2 is a cross-sectional view takenalong the line II-II of FIG. 1. FIG. 3 illustrates an example of a widthand a thickness of a front electrode.

As shown in FIG. 1, a solar cell 1 according to an embodiment of theinvention includes a substrate 10, an emitter layer 20 on a surface(hereinafter, referred to as “a front surface”) of the substrate 10 onwhich light is incident, a transparent conductive oxide layer 30 on theemitter layer 20, a first electrode part 40 (hereinafter, referred to as“a front electrode part”) that is formed on the transparent conductiveoxide layer 30 and electrically connected to the transparent conductiveoxide layer 30, and a second electrode 50 (hereinafter, referred to as“a rear electrode”) that is formed on a surface (hereinafter, referredto as “a rear surface”) of the substrate 10, on which the light is notincident, opposite the front surface of the substrate 10 and iselectrically connected to the substrate 10.

The substrate 10 is formed of a first conductive type silicon, forexample, p-type silicon, though not required. Silicon used in thesubstrate 10 is crystalline silicon, such as single crystal siliconand/or polycrystalline silicon. If the substrate 10 is of a p-type, thesubstrate 10 may contain impurities of a group III element such as boron(B), gallium (Ga), and indium (In). Alternatively, the substrate 10 maybe of an n-type, and/or be formed of other materials than silicon. Ifthe substrate 10 is of an n-type, the substrate 10 may containimpurities of a group V element such as phosphor (P), arsenic (As), andantimony (Sb).

The emitter layer 20 is formed substantially entirely on the frontsurface of the substrate 10. The emitter layer 20 is formed of amaterial of a second conductive type (for example, an n-type) oppositethe first conductive type of the substrate 10, and the semiconductormaterial (or a material characteristic) of the emitter layer 20 may beone (e.g., amorphous silicon) that is different from the semiconductormaterial (or a material characteristic) of the substrate 10 (e.g.,non-amorphous silicon). Thus, the emitter layer 20 and the substrate 10form a hetero junction as well as a p-n junction. The n-type emitterlayer 20 contains impurities of a group V element such as P, As, and Sb.Reference to different semiconductor material may also refer todifferent forms of a semiconductor material.

A plurality of electron-hole pairs produced by light incident on thesubstrate 10 is separated into electrons and holes by a built-inpotential difference resulting from the p-n junction. Then, theseparated electrons move to an n-type semiconductor, and the separatedholes move to a p-type semiconductor. Thus, if the substrate 10 is ofthe p-type and the emitter layer 20 is of the n-type, the separatedholes and the separated electrons may move to the substrate 10 and theemitter layer 20, respectively.

Because the substrate 10 and the emitter layer 20 form the p-n junctionas described above, the emitter layer 20 may be of the p-type if thesubstrate 10 is of the n-type, unlike the embodiment described above. Inthis case, the p-type emitter layer 20 may contain impurities of a groupIII element such as B, Ga, and In, and the separated electrons and theseparated holes may move to the substrate 10 and the emitter layer 20,respectively.

The transparent conductive oxide layer 30 is a conductive layer based onan oxide layer and transfers carriers (e.g., electrons) moving to theemitter layer 20 to the front electrode part 40. In addition, thetransparent conductive oxide layer 30 may serve as an anti-reflectionlayer. The transparent conductive oxide layer 30 is formed of a materialhaving specific resistance (ρ) lower than the emitter layer 20 andhaving good conductivity and transmittance. For example, the transparentconductive oxide layer 30 may be formed of material selected from thegroup consisting of indium tin oxide (ITO), tin-based oxide (e.g.,SnO₂), AgO, ZnO—Ga₂O₃ (or Al₂O₃), fluorine tin oxide (FTO), and/or acombination thereof. Other materials may be used.

The front electrode part 40, as shown in FIG. 1, includes a plurality offirst electrodes (hereinafter, referred to as “a plurality of frontelectrodes”) 41 and a plurality of current collectors 42.

The plurality of front electrodes 41 are positioned on the transparentconductive oxide layer 30 to be spaced apart from one another at auniform distance, thought not required. Further, the front electrodes 41extend substantially parallel to one another in a fixed direction. Eachof the front electrodes 41 collects carriers (e.g., electrons) moving tothe emitter layer 20 through the transparent conductive oxide layer 30.

The plurality of current collectors 42 are positioned at the same level(or surface) as the front electrodes 41 and are electrically connectedto the front electrodes 41. The current collectors 42 extendsubstantially parallel to one another in a direction crossing the frontelectrodes 41. The current collectors 42 collect carriers received fromthe front electrodes 41 to output the carriers to an external device.

Each of the front electrodes 41 includes first and second conductivelayers 411 and 412, and each of the current collectors 42 includes firstand second conductive layers 421 and 422.

Each of the first conductive layers 411 and 421 is formed using a directprinting method. In a screen printing method, a pattern is formed usingauxiliary means, such as a pattern mask. On the other hand, in thedirect printing method, such a pattern formed in the screen printingmethod is not formed, and the first conductive layers 411 and 421 areformed by directly coating a desired front electrode pattern and adesired current collector pattern on the transparent conductive oxidelayer 30. Examples of the direct printing method include an inkjetprinting method, an electro hydrodynamic (EHD) jet printing method, anoffset printing method, a gravure printing method, a flexo printingmethod, and an aerosol jet printing method.

The first conductive layers 411 and 421 are formed of a conductive metalmaterial. Examples of the conductive metal material include at least oneselected from the group consisting of nickel (Ni), copper (Cu), silver(Ag), aluminum (Al), tin (Sn), zinc (Zn), indium (In), titanium (Ti),gold (Au), and a combination thereof.

A width of each of the first conductive layers 411 and 421 variesdepending on a material used, and also may vary depending on a pattern,a shape, a size, etc., of each of the front electrode 41 and the currentcollector 42. The width and a height of each of the first conductivelayers 411 and 421 may be approximately several μm to several nm.

The second conductive layers 412 and 422 are respectively positioned onthe first conductive layers 411 and 421, and are formed using a platingmethod. The second conductive layers 412 and 422 may be formed of atleast one selected from the group consisting of Ni, Cu, Ag, Al, Sn, Zn,In, Ti, Au, and a combination thereof. Other conductive metal materialsmay be used. In the embodiment, the second conductive layers 412 and 422are formed using an electroplating method. However, other platingmethods, such as an electroless plating method, may be used.

A plating condition for forming the second conductive layers 412 and 422is that plating is performed only on the first conductive layers 411 and421 in consideration of a conductivity difference between thetransparent conductive oxide layer 30 and the first conductive layers411 and 421. More specifically, plating may be performed on a desiredportion, i.e., only on the first conductive layers 411 and 421 byadjusting time required in the plating or a current amount depending onthe conductivity difference between the transparent conductive oxidelayer 30 and the first conductive layers 411 and 421 to form the secondconductive layers 412 and 422.

A thickness of each of the second conductive layers 412 and 422 thusformed varies depending on the material used, time required in theplating, the current amount, etc., and also may vary depending on ashape of the first conductive layers 411 and 421.

A width and a height of each of the second conductive layers 412 and 422may be approximately several μm to several tens of μm.

The first conductive layers 411 and 421 and the second conductive layers412 and 422 formed using different methods, i.e., respectively using thedirect printing method and the plating method have different densities.A density of the second conductive layers 412 and 422 formed using theplating method may be greater than a density of the first conductivelayers 411 and 421 formed using the direct printing method.

Each of the front electrode 41 and the current collector 42 thus formedmay have a width of about 10 μm to 100 μm and a height of about 10 μm to20 μm depending on a material used.

The rear electrode 50 is formed substantially entirely on the rearsurface of the substrate 10. The rear electrode 50 collects carriers(e.g., holes) moving to the substrate 10. The rear electrode 50 isformed of a conductive metal material and may be formed of variousmaterials depending on a formation method. For example, if the rearelectrode 50 is formed using a screen printing method, the rearelectrode 50 may be formed of material selected from the groupconsisting of Ag, Al, and a combination thereof, or a conductive highpolymer mixture. If the rear electrode 50 is formed using an inkjetmethod or a dispensing method, the rear electrode 50 may be formed ofmaterial selected from the group consisting of Ni, Ag, and a combinationthereof. If the rear electrode 50 is formed using a plating method, therear electrode 50 may be formed of material selected from the groupconsisting of Ni, Cu, Ag, and a combination thereof. If the rearelectrode 50 is formed using a deposition method, the rear electrode 50may be formed of material selected from the group consisting of Al, Ni,Cu, Ag, Ti, palladium (Pd), chromium (Cr), tungsten (W), and acombination thereof.

FIG. 3 illustrates changes in characteristics of the front electrodes 41when the front electrodes 41 are formed using the plating method asdescribed above.

The front electrode 41 shown in FIG. 3 was completed by forming thefirst conductive layer 421 in a desired portion using, for example, Agthrough the direct printing method and then forming the secondconductive layer 422 on the first conductive layer 421 using the platingmethod.

The front electrode 41 shown in FIG. 3 had specific resistance ρ ofabout 3.3×10⁻⁶ Ω/cm, a width of about 70 μm, a height of about 15 μm,and a cross-sectional area S of about 953 μm². On the other hand, whenthe front electrode was formed using Ag through a screen printing methodaccording to the related art, the front electrode according to therelated art had specific resistance ρ of about 1×10⁻⁶ Ωcm, a width ofabout 120 μm, and a height of about 30 μm.

As described above, in the embodiment, because the first conductivelayers 411 and 421 are formed using the direct printing method capableof forming a layer having a density greater than a related art layerformed using the screen printing method, the densities of the firstconductive layers 411 and 421 are greater than a density of the relatedart layer, and thus specific resistances of the first conductive layers411 and 421 greatly decrease. Further, cross-sectional areas of thefirst conductive layers 411 and 421 used as a seed layer of a platingprocess for forming the front electrode 41 and the current collector 42decrease, and widths of the first conductive layers 411 and 421 used asthe seed layer decrease.

In addition to the first conductive layers 411 and 421, because thesecond conductive layers 412 and 422 are formed using the plating methodcapable of forming a layer having a density greater than a layer formedusing the direct printing method, specific resistances of the frontelectrode 41 and the current collector 42 further decrease. Thus,electrical conductivities of the front electrode 41 and the currentcollector 42 greatly increase.

Specific resistance of the front electrode 41 was reduced to about ⅓ ofspecific resistance of the related art front electrode because of thesereasons, and also the cross-sectional area of the front electrode 41required to serve as an electrode was reduced to about ⅓ of across-sectional area of the related art front electrode because of areduction in the specific resistance. Thus, the width and the height ofthe front electrode 41 were greatly reduced as compared with the relatedart front electrode.

As above, because the widths of the front electrodes 41 and the currentcollectors 42 formed on the front surface of the substrate 10corresponding to the incident surface are reduced, the light receivingarea of the solar cell 1 increases. Hence, the efficiency of the solarcell 1 is improved. Further, the manufacturing cost of the solar cell 1is reduced because of a reduction in the widths and the heights of thefront electrodes 41 and the current collectors 42. Because the totalheight of the solar cell 1 is reduced, it is easy to perform alaminating process required to manufacture a solar cell module.

An operation of the solar cell 1 according to the embodiment of theinvention having the above-described structure is described below.

When light irradiated to the solar cell 1 is incident on the substrate10 through the transparent conductive oxide layer 30 and the emitterlayer 20, a plurality of electron-hole pairs are generated in thesubstrate 10 by light energy based on the incident light. Theelectron-hole pairs are separated by the p-n junction of the substrate10 and the emitter layer 20, and the separated electrons move to then-type emitter layer 20 and the separated holes move to the p-typesubstrate 10. Then, the electrons moving to the n-type emitter layer 20are collected by the front electrodes 41 through the transparentconductive oxide layer 30 and then move to the current collectors 42.The holes moving to the p-type substrate 10 move to the rear electrode50. When the current collectors 42 are connected to the rear electrode50 using electric wires, current flows therein to thereby enable use ofthe current for electric power. In this case, because the widths of thefront electrodes 41 and the current collectors 42 formed using thedirect printing method and the plating method decreases, the lightreceiving area of the solar cell 1 increases, and thus the efficiency ofthe solar cell 1 is improved.

The solar cell 1 according to the embodiment of the invention mayfurther include a back surface field (BSF) layer between the substrate10 and the rear electrode 50. In this case, the BSF layer is formed ofamorphous semiconductor, such as amorphous silicon, and is more heavilydoped with impurities of the same conductive type as the substrate 10than the substrate 10. Thus, the movement of unwanted carries (e.g.,electrons) to the rear surface of the substrate 10 is prevented orreduced by a potential barrier resulting from a difference betweenimpurity doping concentrations of the substrate 10 and the BSF layer. Inother words, the BSF layer prevents or reduces a recombination and/or adisappearance of the electrons and the holes around the surface of thesubstrate 10.

A method of manufacturing the solar cell 1 according to the embodimentof the invention is described below with reference to FIGS. 4A to 4D.

FIGS. 4A to 4D are cross-sectional views sequentially illustrating eachof stages in a method of manufacturing a solar cell according to anembodiment of the invention.

First, as shown in FIG. 4A, an n-type amorphous silicon thin film isformed on the substrate 10 formed of p-type single crystal silicon toform the emitter layer 20. The emitter layer 20 is formed on thesubstrate 10 using a stacking method, such as a chemical vapordeposition (CVD) method and/or a physical vapor deposition (PVD) method.Other methods may be used for the emitter layer 20.

Before forming the emitter layer 20, a saw damage removal process forremoving a damage generated in the surface of the substrate 10, atexturing process for forming a plurality of uneven portions on thesurface of the substrate 10 to increase an amount of incident light, asubstrate cleaning process, etc., may be performed to thereby improve asurface state of the substrate 10. Since these processes are widelyknown to those skilled in the art, a further description may be brieflymade or may be entirely omitted.

Next, as shown in FIG. 4B, the transparent conductive oxide layer 30 isformed on the emitter layer 20. The transparent conductive oxide layer30 may be formed by coating a paste for the transparent conductive oxidelayer 30 on the emitter layer 20 and then performing a thermal process,a deposition process, such as a sputtering process, or a plating processon the coated paste. The transparent conductive oxide layer 30 may beformed of material selected from the group consisting of indium tinoxide (ITO), tin-based oxide (e.g., SnO₂), AgO, ZnO—Ga₂O₃ (orZnO—Al₂O₃), fluorine tin oxide (FTO), and a combination thereof. Othermaterials may be used.

Next, as shown in FIG. 4C, the plurality of first conductive layers 411of a desired shape for the plurality of front electrodes 41 and theplurality of first conductive layers 421 of a desired shape for theplurality of current collectors 42 are formed in desired portions of thetransparent conductive oxide layer 30 using the direct printing method.The direct printing method used to form the first conductive layers 411and 421 may be one of the inkjet printing method, the DID jet printingmethod, the offset printing method, the gravure printing method, theflexo printing method, and the aerosol jet printing method or others.The first conductive layers 411 and 421 may be formed of at least oneconductive metal material selected from the group consisting of Ni, Cu,Ag, Al, Sn, Zn, In, Ti, Au, and a combination thereof.

The first conductive layers 411 and 421 formed using the direct printingmethod each have a density greater than and specific resistance lessthan a layer formed using the screen printing method. Further, it isdifficult to reduce a width of the layer formed using the screenprinting method to a desired width because of characteristics of thescreen printing method. However, a width of each of the first conductivelayers 411 and 421 formed using the direct printing method is smallerthan a minimum width of the layer formed using the screen printingmethod.

Next, as shown in FIG. 4D, an electroplating process is performed usingeach of the first conductive layers 411 and 421 as a seed layer to formthe second conductive layers 412 and 422 on formation portions of thefirst conductive layers 411 and 421. Hence, the plurality of frontelectrodes 41 each including the first and second conductive layers 411and 412 and the plurality of current collectors 42 each including thefirst and second conductive layers 421 and 422 are completed.

In the electroplating process illustrated in FIG. 4D, plating isperformed only on desired portions (i.e., only on the first conductivelayers 411 and 421) in consideration of conductivity difference using adifference between specific resistances of the first conductive layers411 and 421 and specific resistance of the transparent conductive oxidelayer 30 to form the second conductive layers 412 and 422. Because alayer formed using the plating method has characteristics better than alayer formed using the direct printing method, the densities of thesecond conductive layers 412 and 422 are greater than the densities ofthe first conductive layers 411 and 421.

In the embodiment of the invention, because the direct printing methodand the plating method are used to form the front electrodes 41 and thecurrent collectors 42 instead of the screen printing method, themanufacturing cost of the solar cell 1 is reduced.

In other words, in case of a hetero junction solar cell, because anamorphous semiconductor is stacked on a crystalline semiconductorsubstrate to form an emitter layer, a subsequent process has to beperformed at a low temperature equal to or less than about 200° C. so asto prevent or reduce a damage of the emitter layer at a hightemperature. Accordingly, in the related art, a front electrode wasformed using a low temperature fired paste capable of performing (orenabling) a firing process at a low temperature. However, because thelow temperature fired paste is generally more expensive than a hightemperature fired paste, the manufacturing cost of the related art solarcell is increased, and efficiency of the related art solar cell isreduced because of an increase in the specific resistance of the frontelectrode.

On the other hand, when the front electrodes 41 and the currentcollectors 42 are formed according to the method described in thepresent embodiment, the manufacturing cost of the solar cell 1 isreduced because the expensive low temperature fired paste is not used.

Further, because the direct printing method and the plating methodcapable of forming a layer having a density greater than a layer formedusing the screen printing method are used, the conductivities of thefront electrodes 41 and the current collectors 42 is improved. Hence,the widths of the front electrodes 41 and the current collectors 42 maybe reduced to a desired width without a reduction in a carrier transferrate. As a result, the light receiving area of the solar cell 1increases.

Furthermore, because the plating method may be performed at a normaltemperature and enables a large number of layers to be formed at once,the manufacturing efficiency of the solar cell 1 is improved.

Next, after the front electrodes 41 and the current collectors 42 areformed, the rear electrode 50 is formed substantially on the entire rearsurface of the substrate 10 to complete the solar cell 1 shown inFIG. 1. The rear electrode 50 is formed by coating a rear electrodepaste on the rear surface of the substrate 10 using the screen printingmethod and then firing the rear electrode paste. Other methods, such asa plating method, a physical vapor deposition (PVD) method such as asputtering method and an electron beam (E-beam) evaporation method, anda chemical vapor deposition (CVD) method, may be used.

FIG. 5 is a partial cross-sectional view of a solar cell according to anembodiment of the invention.

As shown in FIG. 5, a solar cell 1 a according to an embodiment of theinvention has a structure similar to the solar cell 1 shown in FIG. 1.Thus, structures and components identical or equivalent to thoseillustrated in FIG. 1 are designated with the same reference numerals,and a further description may be briefly made or may be entirelyomitted. Further, since the solar cell 1 a shown in FIG. 5 has the samedisposition diagram as the solar cell 1 shown in FIG. 1, a dispositiondiagram of the solar cell 1 a is omitted.

The solar cell 1 a according to the embodiment of the invention includesa substrate 10, an emitter layer 20 on a front surface of the substrate10 on which light is incident, a transparent conductive oxide layer 30on the emitter layer 20, a plurality of front electrodes 400 that areformed on the transparent conductive oxide layer 30 and electricallyconnected to the transparent conductive oxide layer 30, and a rearelectrode 50 that is formed on a rear surface of the substrate 10, onwhich the light is not incident, opposite the front surface of thesubstrate 10 and is electrically connected to the substrate 10. Thesolar cell 1 a of FIG. 5 further includes a plurality of currentcollectors, that are electrically connected to the plurality of frontelectrodes 400 and extend substantially parallel to one another in adirection crossing the front electrodes 400, in the same manner as thesolar cell 1 shown in FIG. 1.

Unlike the front electrodes 41 of the solar cell 1 shown in FIG. 1, thefront electrodes 400 of the solar cell 1 a each include one conductivelayer. Further, a height of the front electrode 400 is greater than theheight of the front electrode 41, and thus an aspect ratio of the frontelectrode 400 is greater than an aspect ratio of the front electrode 41.Hence, conductivity of the front electrodes 400 is improved. As aresult, efficiency of the solar cell 1 a is further improved comparedwith the efficiency of the solar cell 1.

FIGS. 6A to 6E are cross-sectional views sequentially illustrating eachof stages in a method of manufacturing the solar cell 1 a according tothe embodiment of the invention.

As shown in FIGS. 6A and 6B, the emitter layer 20 is formed on thesubstrate 10, and then the transparent conductive oxide layer 30 isformed on the emitter layer 20 in the same manner as FIGS. 4A and 4B.

Next, as shown in FIG. 6C, a plurality of plating resist layers 60formed of a polymer-based insulating material are formed on portions ofthe transparent conductive oxide layer 30, except where the frontelectrodes 400 will be formed, using a direct printing method. Hence,portions of the transparent conductive oxide layer 30, on which theplating resist layers 60 are not formed, become exposed. Examples of thedirect printing method includes an inkjet printing method, an EHD jetprinting method, an offset printing method, a gravure printing method, aflexo printing method, and an aerosol jet printing method. The platingresist layers 60 may be formed on the transparent conductive oxide layer30 using other methods other than the direct printing method.

Next, as shown in FIG. 6D, a plating process is performed using theexposed portions of the transparent conductive oxide layer 30 as a seedlayer to form a plating material on the exposed portions of thetransparent conductive oxide layer 30 to a desired thickness. Hence, thefront electrodes 400 are formed.

Next, as shown in FIG. 6E, the plating resist layers 60 are removedusing an etching process to complete the front electrodes 400. In thiscase, an etch stop layer may be formed in a portion where the etchingprocess does not need to be performed, and then the etch stop layer maybe removed after performing the etching process. In the embodiment, athickness of the front electrode 400 varies depending on a materialused, a thickness of the plating resist layer 60, time required in theplating process, etc.

Furthermore, when the front electrodes 400 are formed, the plurality ofcurrent collectors are formed on the transparent conductive oxide layer30 in the same manner as a formation method of the front electrodes 400.

Subsequently, the rear electrode 50 is formed on the rear surface of thesubstrate 10 in the same manner as a formation method of the rearelectrode 50 shown in FIG. 1 to complete the solar cell 1 a shown inFIG. 5.

As above, because the front electrodes 400 are formed using the platingmethod capable of greatly increasing a density of a formation layerwithout using the screen printing method, specific resistance of thefront electrodes 400 is greatly reduced, and conductivity of the frontelectrodes 400 increases as described above with reference to FIGS. 1 to4D. Thus, the front electrodes 400 each having smaller width and heightthan the related art may be formed without a reduction in a carriertransfer rate.

Further, if the front electrodes 400 are formed only in desired portionsusing the plating resist layers 60 formed of the insulating material, anaspect ratio of the front electrode 400 may be greater than the aspectratio of the front electrode 41 shown in FIGS. 1 to 4D.

In other words, because the plating is performed on non-formationportions of the plating resist layers 60 (i.e., the exposed portions ofthe transparent conductive oxide layer 30), a thickness of a platinglayer is formed in proportion to a thickness of the plating resist layer60.

Accordingly, if the thickness of the plating resist layer 60 increases,the front electrode 400 having the thickness equal to or greater thanthe thickness of the plating resist layer 60 may be obtained. Hence, thefront electrode 400 corresponding to a plating layer thicker than thefront electrode 41 including the first and second conductive layers 411and 412 may be obtained by employing (or varying) the thickness of theplating resist layer 60.

As a result, aspect ratios of the front electrode 400 and the currentcollector of the solar cell 1 a are greater than aspect ratios of thefront electrode 41 and the current collector 42 of the solar cell 1.Further, resistances of the front electrode 400 and the currentcollector of the solar cell 1 a are less than resistances of the frontelectrode 41 and the current collector 42 of the solar cell 1.Conductivities of the front electrode 400 and the current collector ofthe solar cell 1 a are greater than conductivities of the frontelectrode 41 and the current collector 42 of the solar cell 1. Thus, theefficiency of the solar cell 1 a is improved compared with the solarcell 1.

As described above, because the front electrodes 400 and the currentcollectors of the solar cell 1 a are formed using the direct printingmethod and the plating method without using a low temperature firedpaste, the manufacturing cost of the solar cell 1 a is greatly reduced.Further, because the plating method capable of processing a large numberof layers at once at a normal temperature is used, the manufacturingefficiency of the solar cell 1 a is improved.

The embodiments in which the front electrodes 41 and 400, and thecurrent collectors 42 are formed using the direct printing method andthe plating method may be applied to other solar cells other than thesolar cells 1 and 1 a illustrated in FIGS. 1 to 6E.

Other solar cells to which the embodiments of the invention are appliedare described below.

FIG. 7 is a partial cross-sectional view of a solar cell according to anembodiment of the invention.

As shown in FIG. 7, a solar cell 1 b according to an embodiment of theinvention, similar to the solar cells 1 and 1 a shown in FIGS. 1 and 5,includes a substrate 10, an emitter layer 20, a transparent conductiveoxide layer 30, a plurality of front electrodes 41 (or 400), and aplurality of rear electrodes 51.

Unlike the solar cells 1 and 1 a shown in FIGS. 1 and 5, the solar cell1 b further includes a transparent conductive oxide layer 31 on a rearsurface of the substrate 10. The transparent conductive oxide layer 31is formed between the substrate 10 and the rear electrodes 51 using thesame formation method as the transparent conductive oxide layer 30.

The transparent conductive oxide layer 31 has functions similar to thetransparent conductive oxide layer 30. More specifically, thetransparent conductive oxide layer 31 is used as a path for transferringcarriers (e.g., holes) moving to the substrate 10 to the plurality ofrear electrodes 51 and serves as an anti-reflection layer.

The plurality of rear electrodes 51 are formed on portions of thetransparent conductive oxide layer 31 using the same formation method asthe front electrodes 41 (or 400). Each of the rear electrodes 51includes a first conductive layer formed using a direct printing methodand a second conductive layer formed using a plating method, or includesa conductive layer formed using a plating method.

The plurality of rear electrodes 51 are mainly positioned in portionsfacing the front electrodes 41 (or 400) and extend substantiallyparallel to one another in a fixed direction (for example, in the samedirection as the front electrodes 41 (or 400)). Further, the rearelectrodes 51 are electrically connected to the transparent conductiveoxide layer 31 and collect carriers transferred through the transparentconductive oxide layer 31.

In the solar cell 1 b, the transparent conductive oxide layers 30 and 31are respectively formed on the front surface and the rear surface of thesubstrate 10, and the plurality of rear electrodes 51 are spaced apartfrom one another in the same manner as the front electrodes 41 (or 400).Because light is incident on the substrate 10 through both the frontsurface and the rear surface of the substrate 10, an amount of lightincident on the solar cell 1 b increases.

The solar cell 1 b may further include a plurality of current collectorsthat are formed on the transparent conductive oxide layer 30 on thefront surface of the substrate 10 and extend in a direction crossing theplurality of front electrodes 41 (or 400), and a plurality of currentcollectors that are formed at an edge of the transparent conductiveoxide layer 31 on the rear surface of the substrate 10 and extend in adirection crossing the plurality of rear electrodes 51. The currentcollectors on the transparent conductive oxide layer 30 have the samestructure as the front electrodes 41 (or 400), and the currentcollectors on the transparent conductive oxide layer 31 have the samestructure as the rear electrodes 51. Thus, when the front electrodes 41(or 400) and the rear electrodes 51 are formed, the current collectorsare formed at corresponding locations.

As described above with reference to FIGS. 1 to 6E, in the solar cell 1b, the manufacturing cost is reduced, manufacturing efficiency isimproved, and operation efficiency is further improved because an amountof light incident on the substrate 10 increases.

Since components of the solar cell 1 b including the transparentconductive oxide layer 31 and the rear electrodes 51 are formed usingthe same manufacturing method as FIG. 1 and FIGS. 4A to 4D or FIG. 5 andFIGS. 6A to 6E, a detailed description of a method of manufacturing thesolar cell 1 b may be briefly made or may be entirely omitted. Further,since the current collectors connected to the front electrodes 41 (or400) and the current collectors connected to the rear electrodes 51 areformed using the same method as the front electrodes 41 (or 400) and therear electrodes 51 when the front electrodes 41 (or 400) and the rearelectrodes 51 are formed, a further description may be briefly made ormay be entirely omitted.

Since a disposition diagram of the solar cell 1 b is substantially thesame as the solar cell 1 shown in FIG. 1, except that the rearelectrodes 51 and the current collectors connected to the rearelectrodes 51 have substantially the same shape as the front electrodes41 and the current collectors 42 of the solar cell 1 shown in FIG. 1,the disposition diagram of the solar cell 1 b is omitted.

A solar cell 1 c according to an embodiment of the invention isdescribed below with reference to FIGS. 8 to 10E. Structures andcomponents identical or equivalent to those illustrated in the solarcells 1, 1 a, and 1 b described above are designated with the samereference numerals, and a further description may be briefly made or maybe entirely omitted. In the solar cell 1 c, both first and secondelectrodes are formed on a rear surface of a substrate 10 on which lightis not incident.

FIG. 8 is a partial perspective view of the solar cell 1 c according tothe embodiment of the invention. FIG. 9 is a cross-sectional view takenalong the line IX-IX of FIG. 8;

The solar cell 1 c shown in FIGS. 8 and 9 includes a substrate 10 formedof crystalline silicon, a plurality of emitter layers 21 and a pluralityof BSF layers 71 on a rear surface of the substrate 10, a passivationlayer 91 on a front surface of the substrate 10, an anti-reflectionlayer 35 on the passivation layer 91, a plurality of first electrodes 45respectively positioned on the plurality of emitter layers 21, and aplurality of second electrodes 55 respectively positioned on theplurality of BSF layers 71.

The plurality of emitter layers 21 on the rear surface of the substrate10 extend substantially parallel to one another in a fixed direction andare formed of amorphous semiconductor such as amorphous silicon.

Because the plurality of emitter layers 21 and the substrate 10 form ap-n junction as described above, the plurality of emitter layers 21contain impurities of a conductive type opposite a conductive type ofthe substrate 10.

The plurality of emitter layers 21 and the plurality of BSF layers 71are alternately formed on the rear surface of the substrate 10. Theplurality of BSF layers 71 extend substantially parallel to one anotheralong the plurality of emitter layers 21.

The BSF layers 71 are formed of amorphous semiconductor such asamorphous silicon. The BSF layers 71 are regions (e.g., p+-type regions)that are more heavily doped with impurities of the same conductive typeas the substrate 10 than the substrate 10.

The movement of electrons to the rear surface of the substrate 10 isprevented or reduced by a potential barrier resulting from a differencebetween impurity doping concentrations of the substrate 10 and the BSFlayers 71. Thus, the BSF layers 71 prevent or reduce a recombinationand/or a disappearance of the electrons and the holes around the surfaceof the substrate 10.

The passivation layer 91 on the front surface of the substrate 10converts defects, like a dangling bond, existing around the surface ofthe substrate 10 into stable bonds to prevent or reduce a recombinationand/or a disappearance of carriers (e.g., holes) moving to the substrate10 resulting from the defects.

In the embodiment, the passivation layer 91 is formed of amorphoussemiconductor, such as amorphous silicon. The passivation layer 91 maybe formed of silicon oxide (SiOx) or silicon nitride (SiNx), forexample.

The anti-reflection layer 35 on the passivation layer 91 reduces areflectance of light incident on the solar cell 1 c and increases aselectivity of a predetermined wavelength band. Hence, the efficiency ofthe solar cell 1 c is improved. The anti-reflection layer 35 is atransparent layer, formed of a transparent material, having a refractiveindex of about 1.8 to 2.2. The anti-reflection layer 35 is formed ofsilicon oxide (SiOx) or silicon nitride (SiNx), for example.

Although the plurality of first electrodes 45 and the plurality ofsecond electrodes 55 are different from each other in a formationlocation, the plurality of first electrodes 45 and the plurality ofsecond electrodes 55 have the same structure as the first electrode 41of the solar cell 1 illustrated in FIGS. 1 and 2. Thus, each of thefirst electrodes 45 includes a first conductive layer 451, and a secondconductive layer 452 on the first conductive layer 451, and each of thesecond electrodes 55 includes a first conductive layer 551, and a secondconductive layer 552 on the first conductive layer 551.

The first conductive layers 451 and 551 are formed of at least oneconductive metal material selected from the group consisting of Ni, Cu,Ag, Al, Sn, Zn, In, Ti, Au, and a combination thereof, or a transparentconductive material, such as Al-doped ZnO (AZO) and ITO, using a directprinting method. A width and a height of each of the first conductivelayers 451 and 551 may be approximately several μm to several nm.

The second conductive layers 452 and 552 are respectively formed on thefirst conductive layers 451 and 551 through a plating method (forexample, an electroplating method) using the first conductive layers 451and 551 as a seed layer. The second conductive layers 452 and 552 areformed of at least one conductive metal material selected from the groupconsisting of Ni, Cu, Ag, Al, Sn, Zn, In, Ti, Au, and a combinationthereof.

The plurality of first electrodes 45 collect carriers moving to theemitter layers 21, and the plurality of second electrodes 55 collectcarriers moving through the BSF layers 71.

As described above, because the first electrodes 45 and the secondelectrodes 55 are formed using the direct printing method and theplating method, a density of each of the first and second electrodes 45and 55 increases as described above with reference to FIGS. 1 and 2.Hence, a carrier transfer rate of each of the first and secondelectrodes 45 and 55 increases. As a result, the efficiency of the solarcell 1 c is improved. Further, because an electrode density of the rearsurface of the substrate 10 is reduced by a reduction in the width ofeach of the first and second electrodes 45 and 55, the number of firstelectrodes 45 and the number of second electrodes 55 can increase. Thus,the carrier transfer efficiency of the solar cell 1 c is improved.

FIGS. 10A to 10E are cross-sectional views sequentially illustratingeach of stages in a method of manufacturing the solar cell 1 c accordingto the embodiment of the invention.

First, as shown in FIG. 10A, amorphous silicon is stacked on thesubstrate 10 formed of first conductive type crystalline silicon to formthe passivation layer 91. Then, as shown in FIG. 10B, silicon oxide(SiOx) or silicon nitride (SiNx) is stacked on the passivation layer 91to form the anti-reflection layer 35. The passivation layer 91 and theanti-reflection layer 35 may be formed using a CVD method or a PVDmethod, for example.

Next, as shown in FIGS. 10C and 10D, a stack prevention layer or a maskis positioned on a corresponding portion of the rear surface of thesubstrate 10, and then amorphous silicon containing second conductivetype impurities is stacked on exposed portions of the rear surface ofthe substrate 10, on which the stack prevention layer or the mask is notpositioned, to form the plurality of emitter layers 21 and the pluralityof BSF layers 71. Then, the stack prevention layer or the mask isremoved. The emitter layers 21 and the BSF layers 71 may be formed usinga PECVD method or a sputtering method, for example. The stacking orderof the emitter layers 21 and the BSF layers 71 may vary.

Next, as shown in FIG. 10E, the first conductive layers 451 and 551 arerespectively formed on the emitter layers 21 and the BSF layers 71 usingthe direct printing method, similar to the process illustrated in FIC.4C. The first conductive layers 451 and 551 are formed of a transparentconductive material or a conductive metal material.

Next, similar to the description illustrated in FIC. 1, the transparentconductive material or the conductive metal material is plated on thefirst conductive layers 451 and 551 using an electroplating method usingthe first conductive layers 451 and 551 as a seed layer to form thesecond conductive layers 452 and 552. Hence, the plurality of firstelectrodes 45 and the plurality of second electrodes 55 are formed tocomplete the solar cell 1 c shown in FIGS. 8 and 9.

A solar cell 1 d according to an embodiment of the invention isdescribed below with reference to FIGS. 11 and 13E. Structures andcomponents identical or equivalent to those illustrated in the solarcells 1, la, 1 b, and 1 c described above are designated with the samereference numerals, and a further description may be briefly made or maybe entirely omitted. In the solar cell 1 d, both first and secondelectrodes are formed on a rear surface of a substrate 10 on which lightis not incident.

FIG. 11 is a partial perspective view of the solar cell 1 d according tothe embodiment of the invention. FIG. 12 is a cross-sectional view takenalong the line XII-XII of FIG. 11. The solar cell 1 d shown in FIGS. 11and 12 has substantially the same structure as the solar cell 1 c shownin FIGS. 8 and 9, except a structure of each of a plurality of firstelectrodes and a plurality of second electrodes.

The solar cell 1 d shown in FIGS. 11 and 12 includes a substrate 10formed of crystalline silicon, a plurality of emitter layers 21 and aplurality of BSF layers 71 on a rear surface of the substrate 10, apassivation layer 91 on a front surface of the substrate 10, ananti-reflection layer 35 on the passivation layer 91, a plurality offirst electrodes 45 a respectively positioned on the plurality ofemitter layers 21, and a plurality of second electrodes 55 arespectively positioned on the plurality of BSF layers 71.

The plurality of first electrodes 45 a and the plurality of secondelectrodes 55 a have the same structure as the front electrode 400 ofthe solar cell 1 a illustrated in FIG. 5. Thus, the first electrodes 45a and the second electrodes 55 a each include one conductive layer,unlike the first and second electrodes 45 and 55 of the solar cell 1 cillustrated in FIGS. 8 and 9. An aspect ratio of the first and secondelectrodes 45 a and 55 a is greater than an aspect ratio of the firstand second electrodes 45 and 55. Thus, conductivity of the first andsecond electrodes 45 a and 55 a is improved, and the efficiency of thesolar cell 1 d is improved.

A method of manufacturing the solar cell 1 d is described below withreference to FIGS. 13A to 13E as well as FIGS. 10A to 10D. FIGS. 13A to13E are cross-sectional views sequentially illustrating each of stagesin a method of manufacturing the solar cell 1 d according to theembodiment of the invention.

First, as shown in FIGS. 10A to 10D, the passivation layer 91, theanti-reflection layer 35, the plurality of emitter layers 21, and theplurality of BSF layers 71 are formed on the substrate 10.

Next, as shown in FIG. 13A, a conductive layer 80 is formed on theentire rear surface of the substrate 10, on which the plurality ofemitter layers 21 and the plurality of BSF layers 71 are formed, using aCVD method or a PVD method. The conductive layer 80 is formed of atransparent conductive material or a conductive metal material and has aheight of about several μm to several nm.

Next, as shown in FIG. 13B, plating resist layers 60 formed of aninsulating material are formed on portions of the conductive layer 80using the direct printing method. Hence, portions of the conductivelayer 80, on which the plating resist layers 60 are not formed, areexposed to the outside. Alternatively, the plating resist layers 60 maybe formed on the conductive layer 80 using other methods instead of thedirect printing method.

Next, as shown in FIG. 13C, similar to the process illustrated in FIG.6D, a plating process is performed using the exposed portions of theconductive layer 80 as a seed layer to form a plating material on theexposed portions of the conductive layer 80 to a desired thickness.Hence, the first and second electrodes 45 a and 55 a are formed. Theformation thicknesses of the first and second electrodes 45 a and 55 avary depending on a material used, a thickness of the plating resistlayer 60, time required in the plating process, etc.

Next, as shown in FIGS. 13D and 13E, etch stop layers 65 are formed onthe first and second electrodes 45 a and 55 a, and then the exposedplating resist layers 60 and the portions of the conductive layer 80underlying the exposed plating resist layers 60 are sequentiallyremoved. The exposed plating resist layers 60 and the portions of theconductive layer 80 underlying the exposed plating resist layers 60 maybe removed through a dry or wet etching process.

Next, the etch stop layers 65 are removed to complete the solar cell 1 dshown in FIGS. 11 and 12.

As described above, in the solar cells according to the embodiments ofthe invention, the first and second electrodes may be formed on the samesurface of the substrate. Hence, because at least one of the first andsecond electrodes is formed using the plating process, the widths of thefirst and second electrodes decrease and the size of the light receivingportion of the solar cell increases. Thus, the efficiency of the solarcell is improved.

Furthermore, because the density of the electrode formed using theplating process increases, the conductivity of the electrode isimproved. Thus, the efficiency of the solar cell is further improved.

In addition, because the expensive low temperature fired paste is notused to form the first and second electrodes, the manufacturing cost ofthe solar cell is reduced.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the scope of the principles of thisdisclosure. More particularly, various variations and modifications arepossible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A solar cell, comprising: a single crystallinesemiconductor substrate having a first type conductivity; a non-singlecrystalline emitter layer formed on a front surface of the singlecrystalline semiconductor substrate, wherein the non-single crystallineemitter layer has a second type conductivity opposite of the first typeconductivity; a first transparent conductive oxide layer positioned onthe non-single crystalline emitter layer; a second transparentconductive oxide layer positioned over a rear surface of the singlecrystalline semiconductor substrate; a first electrode part positionedon the first transparent conductive oxide layer and electricallyconnected to the non-single crystalline emitter layer, wherein the firstelectrode part includes a plurality of first electrodes spaced apartfrom one another in a first direction and a first electrode collector ina second direction crossing the first direction; and a second electrodepart positioned on the second transparent conductive oxide layer andelectrically connected to the rear surface of the single crystallinesemiconductor substrate, wherein the second electrode part includes aplurality of second electrodes spaced apart from one another in thefirst direction and a second electrode collector in the second directioncrossing the first direction, wherein the first electrode part includesa first metal layer directly positioned on the first transparentconductive oxide layer and a first plated layer positioned on the firstmetal layer, and electrically connected to the non-single crystallineemitter layer, wherein the second electrode part includes a second metallayer directly positioned on the second transparent conductive oxidelayer and a second plated layer positioned on the second metal layer,and electrically connected to the single crystalline semiconductorsubstrate, wherein the first electrode part and the second electrodepart include at least one of Ni, Cu, Ag, Al, Sn, Zn, In, Ti and Au,wherein the first transparent conductive oxide layer and the first metallayer have different conductivities, and wherein the second transparentconductive oxide layer and the second metal layer have differentconductivities.
 2. The solar cell of claim 1, wherein a density of eachof the first metal layer and the second metal layer is different from adensity of each of the first plated layer and the second plated layer.3. The solar cell of claim 2, wherein the density of the first platedlayer is greater than the density of the first metal layer, and whereinthe density of the second plated layer is greater than the density ofthe second metal layer.
 4. The solar cell of claim 1, wherein at leastone of the plurality of first electrodes and the plurality of secondelectrodes has specific resistance of about 3.3×10⁻⁶ Ωcm.
 5. The solarcell of claim 1, wherein at least one of the plurality of firstelectrodes and the plurality of second electrodes has a width of about10 μm to 100 μm.
 6. The solar cell of claim 1, wherein the non-singlecrystalline emitter layer is formed of amorphous silicon.
 7. The solarcell of claim 1, wherein the first electrode part and the secondelectrode part face each other.
 8. The solar cell of claim 1, wherein atleast one of the front surface and the rear surface of the singlecrystalline semiconductor substrate includes a textured surface.
 9. Thesolar cell of claim 1, wherein sides of the first electrode part and thesecond electrode part are substantially perpendicular relative to thefront surface and the rear surface, respectively.
 10. The solar cell ofclaim 1, further comprising a back surface field layer positioned on therear surface of the single crystalline semiconductor substrate, andwherein the second electrode part is electrically connected to thesingle crystalline semiconductor substrate through the back surfacefield layer.
 11. The solar cell of claim 10, wherein the first platedlayer directly contacts a side surface of the first metal layer and thefirst transparent conductive oxide layer, and wherein the second platedlayer directly contacts a side surface of the second metal layer and thesecond transparent conductive oxide layer.
 12. The solar cell of claim11, wherein the first and second transparent conductive oxide layers areformed of a material selected from the group consisting of indium tinoxide (ITO), tin-based oxide, SnO₂, AgO, ZnO—Ga₂O₃, Al₂O₃, fluorine tinoxide (PTO), and a combination thereof.
 13. The solar cell of claim 1,wherein at least one of the plurality of first electrodes and theplurality of second electrodes has a height of about 10 μm to 20 μm. 14.The solar cell of claim 1, wherein a width of the first electrodecollector is wider than a width of the plurality of first electrodes,and wherein a width of the second electrode collector is wider than awidth of the plurality of second electrodes.
 15. A solar cellcomprising: a single crystalline semiconductor substrate formed of afirst conductive type semiconductor; a plurality of non-singlecrystalline emitter layers formed on a rear surface of the singlecrystalline semiconductor substrate, wherein the plurality of non-singlecrystalline emitter layers have a second conductive type semiconductordifferent from the first conductive type semiconductor, and theplurality of non-single crystalline emitter layers form a heterojunction as well as a p-n junction with the single crystallinesemiconductor substrate; a plurality of first electrodes electricallyconnected to the plurality of non-single crystalline emitter layers; aplurality of back surface field layers formed on the rear surface of thesingle crystalline semiconductor substrate, wherein the plurality ofback surface field layers have the first type conductivity semiconductormore heavily doped than the single crystalline semiconductor substrate;and a plurality of second electrodes electrically connected to theplurality of back surface field layers, wherein the plurality of firstelectrodes include a first metal layer directly positioned on theplurality of non-single crystalline emitter layers and a first platedlayer positioned on the first metal layer, wherein the plurality ofsecond electrodes include a second metal layer directly positioned onthe plurality of back surface field layers and a second plated layerpositioned on the second metal layer, wherein the single crystallinesemiconductor substrate is formed of single crystalline silicon and theplurality of non-single crystalline emitter layers are made ofnon-single crystalline silicon, and wherein the plurality of backsurface field layers are made of non-single crystalline silicon.
 16. Thesolar cell of claim 15, wherein a density of the first plated layer isgreater than a density of the first metal layer, and wherein a densityof the second plated layer is greater than a density of the second metallayer.
 17. The solar cell of claim 15, wherein the rear surface of thesingle crystalline semiconductor substrate, on which the plurality offirst electrodes and the plurality of second electrodes are positioned,is opposite a front surface of the single crystalline semiconductorsubstrate.
 18. The solar cell of claim 15, further comprising apassivation layer positioned on a front surface of the singlecrystalline semiconductor substrate which is a light incident surface.19. The solar cell of claim 18, further comprising an anti-reflectionlayer positioned on the passivation layer.
 20. The solar cell of claim15, wherein the first plated layer is covering a side surface of thefirst metal layer, and wherein the second plated layer is covering aside surface of the second metal layer.
 21. The solar cell of claim 15,wherein at least one of the plurality of first electrodes and theplurality of second electrodes has a width of about 10 μm to 100 μm. 22.The solar cell of claim 15, wherein the plurality of non-singlecrystalline emitter layers are formed in parallel, and wherein theplurality of back surface field layers are formed in parallel.
 23. Thesolar cell of claim 15, wherein the plurality of non-single crystallineemitter layers and the plurality of back surface field layers arealternately formed on the rear surface of the single crystallinesemiconductor substrate.
 24. The solar cell of claim 15, wherein thefirst plated layer is positioned on a side surface of the first metallayer, and wherein the second plated layer is positioned on a sidesurface of the second metal layer.
 25. The solar cell of claim 15,wherein a width of the first plated layer is wider than a width of thefirst metal layer, and wherein a width of the second plated layer iswider than a width of the second metal layer.
 26. The solar cell ofclaim 15, wherein the first plated layer is not positioned on a sidesurface of the first metal layer, and wherein the second plated layer isnot positioned on a side surface of the second metal layer.
 27. Thesolar cell of claim 18, wherein the passivation layer includes siliconnitride or silicon dioxide.
 28. The solar cell of claim 19, wherein theanti-reflection layer includes silicon nitride or silicon dioxide. 29.The solar cell of claim 15, wherein at least one of the plurality offirst electrodes and the plurality of second electrodes has a height ofabout 10 μm to 20 μm.
 30. The solar cell of claim 15, wherein theplurality of first electrodes and the plurality of second electrodesinclude at least one of Ni, Cu, Ag, Al, Sn, Zn, In, Ti and Au.
 31. Thesolar cell of claim 10, wherein the back surface field layer is formedof amorphous silicon.
 32. The solar cell of claim 15, wherein theplurality of non-single crystalline emitter layers or the plurality ofback surface field layers are formed of amorphous silicon.